Synthetic bulk element having thin ferromagnetic film switching characteristics



Sept. 30, 1969 OBERG 3,470,550

SYNTHETIC BULK ELEMENT HAVING THIN I-PIRROMAGNE'IIC FILM SWITCHING CHARAII'IERTSTFCT Filed June 16, 1967 2 Sheets-$heet l INvENToR PAUL E. GEE/P6 Sept. 30, 1969 P. E. OBERG 3,470,550

SYNTHETIC BULK ELEMENT HAVING THIN FERROMAGNETIC FILM SWITCHING CHARACTERISTICS 2 Sheets-Sheet.

Filed June 16, 1967 INVENTOR BY AT PAUL E. OBERG United States Patent 3,470,550 SYNTHETIC BULK ELEMENT HAVING THIN FERROMAGNETIC FILM SWITCH- ING CHARACTERISTICS Paul E. ()berg, Minneapolis, Minn., assignor to Sperry Rand Corporation, New York, N.Y., a corporation of Delaware Filed June 16, 1957, Ser. No. 646,638 lint. Cl. Gllc 7/00, 11/14 US. Cl. 340-174 8 Claims ABSTRACT OF THE DISCLOSURE An element that may be utilized as a transformer, or inductor, core or as a bistable memory core comprising a plurality of stacked, superposed layers of thin-ferromagnetic-films separated by interstitial layers of insulating material. The thin-ferromagnetic-film layers preferably possess low anisotropic fields H with portions of alternate layers having a high coercivity H for functioning as permanent magnets. The permanent magnet portions, having their magnetization aligned along a SN permanent magnetic axis M bias the magnetization of the low H anisotropic regions: to become aligned With the polarization of the magnetization of the permanent magnet portions; or to become rotated out of alignment with their easy axes that are orthogonal to the axis M Operation as a transformer, or inductor core is achieved by the application and detection of an AC field along a magnetic axis that is orthogonal to the axis M and to the easy axis of the low H anisotropic regions while operation as a memory core is achieved by the application of drive fields and the detection of switching fields along a magnetic axis that is orthogonal to the axis M but parallel to the orthogonally oriented easy axes of the low H anisotropic regions.

Background of the invention The present invention relates to magnetizable elements comprising a plurality of stacked, magnetizable layers of thin-ferromagnetic-films, each layer possessing singledomain property. The term single-domain property may be considered the magnetic characteristic of a three-di mensional element of magnetizable material having a thin dimension that is substantially less than the Width and length thereof wherein no magnetic domain walls can exist parallel to the large surfaces of the element. Such layers may, or may not, possess the magnetic characteristic of unaxial anisotropy providing an easy axis along which the remanent magnetization thereof lies in a first or a second and opposite direction. The term magnetizable material shall designate a substance having a remanent magnetic fiux density that is substantially high, i.e., approaches the flux density at magnetic saturation. It is desirable that each of the several thin-ferromagneticfilm layers layers that make up the magnetizable element possess such single-domain property whereby singledomain rotational switching of the magnetization M of such magnetizable element shall be achieved in a manner such as described in the S. M. Rubens et al., Patent No. 3,030,612. Such magnetizable elements may be fabricated in a continuous vapor deposition process such as disclosed in the S. M. Rubens et al., Patent No. 2,900,282 and Patent No. 3,155,586. However, such magnetizable elements may be formed by any one of the plurality of well known methods of fabricating magnetizable memory elements, e.g., cathodic sputtering.

As a thin-ferromagnetic-filrn layer possessing this single-domain property is limited in its maximum thickness to the order of 10,000 Angstroms (A.) is apparent that the net flux, which is a function of its cross sectional area,

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is limited. Accordingly, it is desirable to have a magnetizable element that is capable of operating in a single-domain manner while providing substantially larger external magnetic fields, or closed path flux, that, upon the switching or rotation of the elements magnetization M, couple the lines associated therewith producing an output signal therein that is of a substantially larger magnitude than that achieved by a single thin-ferromagnetic-film layer. Prior art arrangements of magnetizable elements operating as a single element have comprised a plurality of stacked, similar magnetizable layers of thin-ferrornagnetic-films separated by interstitial layers of insulating material involving all such magnetizable. elements wherein the easy axes of all of the thin-ferromagnetic-film layers thereof are aligned with the materials thereof being similar.

Prior art arrangements of magnetizable elements operating as a single element comprise a plurality of stacked, similar magnetizable layers of thin-ferromagneticfilms separated by interstitial layers of insulating material that are fabricated with the easy axes of all magnetizable layers aligned. However, if it is desired that the magnetizable layers should rotate in a single-domain manner it is essential that the total thickness of the magnetizable element be limited to a substantially thin dimension. The reason for this is that when the magnetization M in the many magnetizable layers rotates such layers magnetization M vectors rotate in the same direction. Thus, the components of M that are perpendicular to the major surfaces of the layers are all in the same aligned direction through the thickness thereof tending to be continuous in the magnetizable and insulating layers. In other words, internal pole pairs, i.e., on opposite surfaces on each insulating layer, tend to cancel out each other leaving only the oles on the top and bottom layers uncancelled. This results in a small demagnetizing field, i.e., the field applied to the magnetizable layer that tends to demagnetize the layers normal magnetization for the large thickness that is produced by the many magnetizable and insulating layers. This small demagnetizing field approaches that of bulk magnetizable material of the same thickness causing the magnetizable layers to switch in a manner similar to bulk material switching.

In contrast to this prior art arrangement, by utilizing the present invention the magnetization M in the adjacent magnetizable layers rotate in opposite directions whereby the components of M that are perpendicular to the major surfaces of the layers are in opposite, but aligned directions perpendicular to the thickness of the element. In this arrangement the internal ole pairs do not tend to cancel out each other. This results in a very large normal demagnetizing field on each magnetizable layer for the large thickness produced by the many magnetizable and insulating layers. This large demagnetizing field forces the magnetization M of the individual magnetizable layers to switch in a single-domain manner similar to that achieved by magnetizable elements of a single thin-ferromagnetic-film layer. When this large demagnetizing field is present the magnetization M vector remains essentially in the plane of the magnetizable layer during its rotation. This is a requirement, and the reason, for the high speed change in magnetization provided by singledomain films.

Summary of the invention The present invention is an improvement of such above prior art arrangements of magnetizable elements comprising a plurality of stacked, similar magnetizable layers of thin-ferromagnetic-films that are separated by interstitial layers of insulating material. All of the magnetizable layers of the present invention are preferably of substantially the same thickness and possess the magnetic characteristic of single-domain roperty. Additionally, all of the magnetizable layers of the present invention are of substantially the same material except that portions of alternate layers of the thin-ferromagnetic-films have a high coercivity H e.g., H l oersteds for an approximately 90% C0-10% Fe layer, for functioning as permanent mag- -*nets. The permanent magnet portions of these alternate layers have their magnetization aligned along a SN permanent magnet axis M providing a biasing field aligned parallel, in the same direction, in the remaining low anisotropic portion of the layer having the high coercivity portion, but aligned antiparallel, or NS, in the low anisotropic other alternate layer. Thus, alternate magnetizable layers forming a first set of layers are formed having a first high coercivity H portion and a second low anisotropic field H portion While the other alternate magnetizable layers forming a second set of layers are formed with a low anistropic field H e.g., H 4.0 oersteds for an approximately 80% Ni-20% Fe layer.

The magnetizable elements of the present invention are presented as having two preferred embodiments: one having the ability to be operated as a transformer, or inductor, core; while the second embodiment has the ability to be operated as a bistable memory core. In the first embodiment, that operated as an inductor core, operation is achieved by the application of an AC driving field along a magnetic axis that is orthogonal to the permanent magnet axis M of the first set of layers and to the easy axis of the low I-I material portion While detection of the AC field is also achieved along the magnetic axis that is orthogonal to such permanent magnet axis M and to the easy axis of the low H material portion. Operation as a bistable memory core is achieved by the utilization of device that is similar to that utilized as an inductor core in that the device to be utilized as a bistable memory core is preferably fabricated having low values of unaxial anisotropy H providing a low H easy axes in the low anisotropic field H regions, those regions other than the permanent magnet regions, that are orthogonal to the permanent magnet axis M Operation of this second embodiment as a bistable memory core is achieved by the application of a drive field along a magnetic axis that is orthogonal to the permanent magnetic axis M or parallel to the easy axis of the associated low anisotropic field region, while readout is achieved by the detection of a switching field along a magnetic axis that is orthogonal to the magnetic axis M or parallel to such easy axis of the low anisotropic field region.

Drive and sense lines, or windings, that are magnetically, or conductively, coupled tot he magentizable elements of the present invention may be of the well known printed circuit type as particularly adapted in bistable memory core operation or more conventional transformer winding techniques when operated as an inductor core.

Brief description of the drawings FIG. 1 is a side view of a magnetizable element of a plurality of magnetizable layers separated by interstitial layers of insulating material as proposed by the present invention.

FIG. 2 is a plan view of the magnetizable element of FIG. 1 illustrating the construction and orientation of the permanent magnet axis M of the high coercivity region.

FIG. 3 is a schematic illustration of the related vectors involved in the switching mechanism of adjacent magnetizable layers as proposed by the present invention.

FIG. 4 is a plan view of a magnetizable element of the present invention illustrating the orientation of the permanent magnet axis M and of the magnetization M of the low anisotropic field regions of the inductor core.

FIG. 5 is a plan view of a magnetizable element of the present invention illustrating the orientation of the ermanent magnet axis M and the magnetization M of the low anisotropic field regions of the bistable memory core.

FIG. 6 is a composite illustration of the B-H loop characteristics of the magnetizable elements of FIG. 4 and of FIG. 5.

Description of the preferred embodiment With particular reference to FIG. 1 there is illustrated a side view of a magnetizable element that incorporates the inventive concept of the present invention. Magnetizable element 10 is comprised of a substrate 12 and a plurality of magnetizable layers 14, 16 insulatively separated by a plurality of insulating layers 18. Magnetizable element 10 is particularly adaptable to be fabricated in successive deposition steps of alternate layers of magnetizable material and insulating material in an evacuatable enclosure. Magnetizable element 10 is preferably fabricated in a continuous vapor deposition process such as disclosed in the S. M. Rubens et al. Patents Nos. 2,900,- 282 and 3,155,561 or the A. V. Pohm Patent No. 3,065,- 105. The multi-layer element 10 may be deposited upon a substrate 12 of many well known materials such as glass or metal.

All of the magnetizable layers of the present invention are preferably of substantially the same thickness and possess the magnetic characteristic of single-domain property whereby by the application of the proper drive fields single-domain rotational switching of the magnetization of such layers may be achieved in the manner such as described in the S. M, Rubens Patent No. 3,030,612. Additionally, all of the magnetizable layers of the present invention are of substantially the same material except that alternate layers 14 have a high coercivity H portion 20 for functioning as a permanent magnet. The remaining portions 22 of magnetizable layers 14 and all of the magnetizable layers 16 being of substantially the same material; preferably being lo'w anisotropic field I-I materials. The permanent magnet portions 20 of alternate layers 14 have their magnetization permanently aligned along a S-N permanent magnet axis M providing a biasing field aligned in the same direction in the remaining low anisotropic portions 22 of layers 14 but aligned antiparallel, or NS, in the low anisotropic alternate layers 16. Thus, alternate magnetizable layers 14a, 14b, 14c and 14d forming a first set of layers are formed having a first high coercivity H portion and a second low anisotropic field H portion while the other alternate magnetizable layers 16a, 16b, 16c and 16d forming a second set of layers are formed with a low anisotropic field H With particular reference to FIG. 2 there is illustrated a plan view of the magnetizable element 10 of FIG. 1 for purposes of illustrating the orientation of the permanet magnet axis M associated with portions 20 of layers 14. For purposes of providing an illustrative example it has been determined by applicant that with an element 10 having an overall length L having a feathering edge width E, in which the portions 20, 22 of layers 14 merge, the distance between the center of the feathering edge E to the edge of element 10, noted as L may be much less than /3 of L In this embodiment the low anisotropic field portions may be of approximately Fe-20% Ni having an H equal to three oersteds (3 oe.) while the high coercivity portions 20 of layers 14 may be of high percentage of Cobalt having an H, of 10 oersteds (l0 oe.) or greater. Note: For ease of subsequent discussion, the

vector magnetization M, either aligned along, or rotated out of alignment with the associated easy axis, and the associated easy axis M shall be identified by similar terms; i.e., magnetization M of layer 14 having an easy axis M With particular reference to FIG. 3 there is presented a diagrammatic illustration of the paths traced out by the magnetization vectors M M of magnetizable layers 14, 16. As discussed above, the present invention relates to a magnetizable element that comprises a plurality of: stacked, superposed, magnetizable layers of thin-ferromagnetic-films separated by interstitial layers of insulating; material. As an example, in the embodiment of FIG. 5 thelow anisotropic field H magnetizable layers possess the,

magnetic property of uniaxial anisotropy providing an easy axis whereby alternate magnetizable layers have their easy axes aligned but their magnetization biased by a permanent magnet along two respectively different axes M and M forming a means axis of magnetization M that is intermediate the two axes of the two sets of alternate magnetizable layers. Each of the layers of low anisotropic field H magnetizable material, such as portion 21) of layer 14 and adjacent layer 16 possess single-domain properties that are capable of having their magnetization switched, or rotated, in a single-domain manner such as disclosed in the above referenced S. M. Rubens et al. Patent No. 3,030,612.

In the magnetization M as in magnetizable layer 16, is affected by an applied drive field H along the mean axis M,,, or line 32, in the plane of the layer the magnetization M is induced to rotate in the direction away from the applied drive field H toward a position M through an angle When the magnetization begins to rotate out of alignment with its easy axis M there is generated a component M which is normal to the plane of the magnetizable layer. However, the demagnetizing field of the magnetizable layer 16 limits this normal component to extremely small values causing the magnetization M to rotate through path 30 which path is substantially in the plane of layer 16. This mechanism is more fully discussed in the text Amplifier and Memory Devices: With Films and Diodes McGraw-Hill Book Company, 1965, chapter 13.

With a plurality of magnetizable layers 16 arranged in a stacked, superposed arrangement similar to that of FIG. 1 with the easy axes of all such layers 16 aligned, an applied drive field H would cause the magnetization M of all such layers 16 to rotate in the same direction. Thus, the components M that are perpendicular to the major surfaces of layer 16 are all in the same aligned direction through the plurality of layers tending to be continuous therethrough. In other words, these adjacent layers 16 would form internal pole pairs with respect to adjacent layers 16, such as components M that tend to cancel out each other leaving only the poles on the top and bottom layers 16 uncancelled. This results in a very small demagnetizing field M for the relatively large thickness through the plurality of layers 16. This very small demagnetizing field approaches that of bulk magnetizable material of the same thickness causing the magnetization of the plurality of magnetizable layers 16 to switch in a manner similar to that of bulk material.

However, if instead of the above, wherein there was provided a plurality of stacked layers 16 having their easy axes aligned, assume that there are provided a like number of magnetizable layers 14 interstitial with the layers 16 forming .adjacent pairs of layers 14 and 16 and further assume that the easy axes of such layers 14 are aligned but biased at an angle 06/2 with the aligned easy axes of the plurality of layers 16. These adjacent pairs of layers 14, 16 may then be assumed to generate an effective, or mean, magnetization axis 32 which bisects the angle a between the biased magnetization M M associated with layers 14, 16 respectively. Now, if a drive field H is applied parallel to the planes of the layers 14, 16 and of an opposite polarization with respect to the average magnetization M along the mean axis 32 the magnetizations M and M of layers 14 and 16, respectively, are forced to rotate in opposite directions. Thus, as in the example shown in FIG. 3, magnetization M of layer 14 would rotate in a clockwise direction (as viewed from above) along a path 34 while magnetization M in layers 16 would rotate in a counterclockwise direction along path 30. The vertical components M and M generated by the rotation of magnetization M and M of layers 14 and 16, respectively, due to the opposite directions of rotation, would be of substantially equal magnitude but of opposite polarity. Thus, by utilizing the inventive concept of the present invention the magnetization in the adjacent magnetizable layers 14 .and 16 rotate in opposite directions whereby the components of M that are perpendicular to the major surfaces of the layers are in opposite, but aligned, directions through the thickness of the magnetizable element provided by the plurality of pairs of layers 14, 16 and the associated insulating layers 18see FIG. 1. In this arrangement the internal pole pairs, i.e., the M components M and M that are perpendicular to the major surfaces of the layers 14 and 16 do not tend to cancel out each other. This results in a very large demagnetizing field for the large thickness produced by the many magnetizable layers 14, 16 and insulating layers 18. This large demagnetizing field forces the magnetization M of the individual magnetizable layers 14, 16 to switch in a single-domain manner similar to that achieved by magnetizable elements of a single thin-ferromagnetic-film layer. When this large demagnetizing field is present the magnetization M vector of each layer 14, 16 remains essentially in the plane of the associated magnetizable layer 14, 16; this is a requirement, and the reason, for high speed rotational change in magnetization.

With particular reference to FIG. 4 there is illustrated a plan view of a magnetizable element 10a illustrating the orientation of the easy axes M M along line 44 formed by the low anisotropic regions of magnetizable layers 14, 16, respectively, and the permanent magnet axis M along line 44 formed by the high coercivity portions 20 of layers 14. Although the illustrated embodiment will be discussed as magnetizable it is to be understood that this is not essential thereto. A permeable layer having a permeability a greater than that of air i.e., 21, and with substantially no remanent magnetization could function as a transformer, or inductor, core. In this arrangement of FIG. 4, utilizing magnetizable element 10a as a transformer, or inductor, core, the permanent magnet portions 20 of layers 14 having a permanent magnet axis M force the magnetization of the low anisotropic regions 22 to be aligned therewith along line 44 and the magnetization of layers 16 to be aligned antiparallel thereto along line 44. This arrangement is as illustrated in FIG. 1 in which it is shown that adjacent pairs of cores 14, 16 function as high permeability substantially closed flux return paths for each other.

Operation of magnetizable element 10a as an inductor core is achieved by the application and detection of an AC field along a magnetic axis that is orthogonal to the antiparallel magnetization M M and the permanent magnet axis M The AC magnetizing field :H applied along the axis 42 by winding 40 causes the magnetization on M M associated with layers 14, 16 to oscillate about the axis 44 through the respective angles 6 6 The flux variations of magnetizable element 113a, due to the oscillation of the magnetizations M M about axis 44, is detected along magnetic axis 42 by winding 46; as an inductor core only one winding 40 is required. although the two windings 4t), 46 are illustrated for operation as a transformer core. In this arrangement windings 40 and 46 function as primary and secondary windings, respectively, that are inductively coupled to the magnetizable element 10,. By winding 42 coupling a magnetizing force :':H of an intensity (e.g., H =o.g. H just sufficient to cause the magnetizations M M to oscillate i65 about the axis 44, i.e., 0 0 equal to the total flux change in magnetizable element 10,, is equal to approximately 0.9 of the total switchable flux therein.

With particular reference to FIG. 6 there is presented the B-H loop 60 that is an approximate representation of the magnetic flux path traversed by the magnetic flux of magnetizable element 10a when operated in the transformer mode as described with particular reference to FIG. 4. Loop 60 represents the substantially lossless operation of magnetizable element 16a such as is usually associated with the operation of thin-ferromagnetic-film layers when driven in the hard direction. As will be further discussed with particular reference to FIG. 5, loop 62 represents the approximate path traversed by the magnetic flux of element 1% when operated as a memory element in accordance with the embodiment of FIG. 5. Loops 60 and 62 of FIG. 6 are typical BH loops of thin-ferromagnetic-film elements having unaxial anisotropy and being driven in the hard and easy directions, respectively. For a deailed discussion of the rotational loops of FIG. 6 reference may be had to the publication Thin Ferromagnetic Films, A. C. Moore, IRE Transactions on Component Parts, March 1960, pages 3-14.

With particular reference to FIG. 5 there is illustrated a plan view of a magnetizable element b when utilized as a memory element. In this arrangement the magnetization of the high coercivity portions of layers 14 are aligned along the NS permanent magnet axes M while the magnetization M M associated with the low anisotropic regions 22 of layers 14 and of layers 16, respectively, are parallel aligned along an easy axis 52 which is orthogonal to the permanent magnet axis M With the low anisotropic regions 20 of layers 14 and of layers 16 having a preferred direction of magnetization 52 the magnetization thereof, M M would normally be aligned therealong. However, the hard direction biasing fields provided by the magnetization of regions 20 of layers 14, being in antiparallel directions in adjacent layers 14-, 16, cause the magnetization thereof. M M to be biased, ,8 fi out of alignment with their easy axes 52, respectively.

Operation of magnetizable element 10!) of FIG. 5 as a memory element, or bistable core, is achieved by the application of a drive field iH; where +H may be representative of a storing of a 1 and H may be representative of the storing of a O in memory element 10b. This drive field H is coupled to memory element 10b by means of coil 50 providing a drive field H that is oriented parallel to magnetic axis 52 but orthogonal to permanent magnet axis M In this embodiment the applied drive field H is of an intensity in the area of magnetizable element 10b approximating H causing the magnetization M and M to be rotated less than 180, e.g., 120, to assume a magnetization polarization along their oppositely biased axes, e.g., from 1 to 0. The magnetic flux change in magnetizable element 1012 due to the substantial or insubstantial rotation, e.g., from 1 to 0 or from 0 to 0 of the magnetization M M is detected by the output, or sense, coil 56, whose magnetic axis is oriented parallel to the magnetic axis 52, inducing a signal therein that is representative of the informational state of magnetizable element 10b. As an example, with the magnetization M M of the two sets of magnetizable layers 14, 16 of magnetizable element 1012 established in their respectively biased polarization 1, which directions may be representative of the storage of a 1 therein, the application of a H approximately equal to H drive field by winding 50 would cause the magnetization M M thereof to rotate 120. This would induce a substantial signal in output winding 56. Conversely, with the magnetization of the magnetizable layers 14, 16 of magnetizable element 10b established along their biased axes O the application of a +H drive field by winding 50 would induce an insubstantial signal in output winding 56 that may be representative of the storing of a 0 therein.

With particular reference to FIG. 6 there is illustrated the loop 62 that describes the magnetic flux path traversed by the magnetic flux of magnetizable element 10!) when operated as a memory core in accordance with the embodiment of FIG. 5. It can be seen that loop 62 has a substantially rectangular form that approaches the ideal characteristic for a magnetizable memory element.

Thus it is apparent there has been described and illustrated herein a preferred embodiment of the present invention that provides an improved magnetizable element comprising a plurality of stacked, magnetizable layers of thin-ferromagnetic-films that operate in a single-domain manner. It is understood that suitable modifications may be made in the structure as disclosed provided that such modifications come within the spirit and scope of the appended claims. Having, now, fully illustrated and described my invention, what I claim to be new and desire to protect by Letters Patent is set forth in the appended claims.

I claim:

1. A synthetic bulk element operating in a single domain rotational mode, comprising:

a plurality of stacked, superposed layers of thin-ferromagnetic-films having a permeability greater than one and separated by insulating material;

each of said layers possessing the magnetic characteristic of single-domain property;

said layers arranged in first and second sets;

said first set formed by alternate ones of said layers;

said second set formed by alternate ones of said layers,

other than those of said first set;

the layers of said first set having a first high coercivity material region and a second low anisotropic field material region;

the layers of said second set being of a low anisotropic field material;

the first regions of the layers of said first set permanently magnetized along a permanent magnet axis M the magnetization of the first regions of the layers of the first set biasing the magnetization of the low anisotropic field material regions of the layers of said first and second sets toward alignment with said permanent magnet axis M input and output means inductively coupled to said layers having a magnetic axis that is orthogonal to said permanent magnet axis M said input means coupling a drive field +H to said layers for causing the magnetizations of said first and second sets to rotate in a single-domain manner in opposite directions about said permanent magnet axis M for inducing a signal in said output means.

2. A substantially lossless inductor, comprising:

a plurality of stacked, superposed magnetizable layers of thin-ferromagnetic-films separated by interstitial layers of insulating material;

each of said magnetizable layers possessing the magnetic characteristic of single-domain property;

said magnetizable layers arranged in first and second sets;

said first set formed by alternate ones of said magnetizable layers;

said second set formed by alternate ones of said magnetizable layers, other than those of said first set;

the layers of said first set having a first high coercivity material region and second low anisotropic field material region;

the layers of said second set being of a low anisotropic field material;

the first regions of the layers of said first set permanently magnetized along a permanent magnet axis M the magnetization of the first regions of the layers of the first set biasing the magnetization of the low anisotropic field material regions of the layers of said first and second sets into alignment with said permanent magnet axis M and in an anti-parallel relationship with each other;

input and output means inductively coupled to said magnetizable layers having a magnetic axis that is orthogonal to said permanent magnet axis M said input means coupling a drive field :H to said magnetizable layers for causing the magnetization of said first and second sets to oscillate in a singledomain manner opposite directions about said permanent magnet axis M for inducing a signal in said output means.

3. The inductor of claim 2 wherein said drive field H is of an intensity, in the areas of said low anisotropic field regions, of H H 4. The inductor of claim 3 wherein said low anisotropic field regions are approximately 80% Fe=20% Ni having 5 an H of approximately 4.0 oersteds and said high coercivity regions are of a major percentage cobalt having an H of at least 10.0 oersteds.

5. The inductor of claim 2 wherein the anisotropic field H; of said low anisotropic field portions is less than 0.5 oersted.

6. A bistable memory operable in a single domain rotational mode, comprising:

a plurality of stacked, superposed magetizable layers of thin-ferromagnetic-films separated by interstitial layers of insulating material;

each of said magnetizable layers possessing the magnetic characteristic of single-domain property;

said magnetizable layers arranged in first and second sets;

said first set formed by alternate ones of said magnetizable layers;

said second set formed by alternate ones of said magnetizable layers, other than those of said first set;

the layers of said first set having a first high coercivity material region and a second w anisotropic field material region;

the layers of said second set being of a low anisotropic field material;

the first regions of the layers of said first set permanently magnetized along a permanent magnet axis the low anisotropic field regions of said first and second sets having uniaxial anisotropy for providing aligned easy axes along which their magnetization M and M may lie, said aligned easy axes oriented orthogonal to said permanent magnet axis M the magnetization of the first regions of the layers of the first set biasing the magnetization of the low anisotropic field material regions of the layers of said first and second sets out of alignment with their aligned easy axes; input and output means inductively coupled to said magnetizable layers having a magnetic axis that is orthogonal to said permanent magnet axis M said input means coupling a drive field iH to said magnetizable layers for causing the magnetizations of said first and second sets to rotate in a single-domain manner in opposite directions about their said aligned easy axes for inducing a signal in said output means. 7. The memory of claim 6 wherein said drive field H is of an intensity, in the area of said low anisotropic field portions, of H approximately equal to H 8. The memory of claim 6 wherein said input and output means include separate associated windings.

References Cited UNITED STATES PATENTS 6/1963 Moore 340-174 3/1968 Feldtkeller 340-174 XR UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,470 550 September 30 1969 Paul E. Oberg It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 36, should read Column 9, line 5, should read Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. E. JR.

Attesting Officer Commissioner of Patents 

